1. Field
The embodiment(s) discussed herein is directed to a radio base station, a radio terminal and a radio communication method. For examples, the embodiment(s) may be applied to a pre-coding MIMO (Multiple Input Multiple Output) transmission method.
2. Description of the Related Art
MIMO transmission method is one of radio communication techniques that are discussed as LTE (Long Term Evolution) in 3GPP (3rd Generation Partnership Project).
As techniques relating to the MIMO transmission method, one is disclosed in Patent Document 1 below, for example. Patent Document 1 discloses a method of determining a range of wireless resource groups to be allocated for communication according to long-term quality to limit the range of the wireless resource groups, reducing the information quantity of control information when the wireless resource to be used in actual communication is designated, thereby to suppress degradation of the transmission efficiency.
There is pre-coding MIMO transmission method (refer to non-patent document 1 below) as another one of the MIMO transmission methods. In this pre-coding transmission method, the transmission side multiplies a modulation signal by a predetermined weighting factor (weight information) according to known transmission path information, and performs transmission.
Patent Document 2 below discloses a method for use in an MIMO communication system of coding data in accordance with one or more pre-coding schemes, modulating the data, pre-coding modulation symbols on the basis of an equivalent channel response to pre-condition the same, for example. According to this technique, the number of transmission streams and the transmission beams in the MIMO are switched according to the communication environments to optimize the beam forming and the throughput.
[Patent Document 1] Japanese Laid-Open Patent Publication No. 2006-238314
[Patent Document 2] Published Japanese Translation of PCT International Publication for Patent Applications No. 2005-522086
[Non-Patent Document 1] 3GPP TSG RAN WG1 49bis “R1-072843”
In the pre-coding MIMO transmission method, the weight information used at the transmission side is notified to the reception side. In such case, if all the weight information is transmitted, the data transmission efficiency can be reduced. The known techniques do not give any attention to this drawback.